This invention relates to non-human animals deficient in the expression of uridine phosphorylase, and also to their offspring.
Pyrimidine nucleoside phosphorylases are enzymes, which take part in the biosynthesis and degradation of pyrimidine in its metabolism and play an important role of regulating the in vitro nucleoside pool through degradation and synthesis of pyrimidine bases in the salvage pathway. Further, pyrimidine nucleoside phosphorylases in mammals are known to include uridine phosphorylase and thymidine phosphorylase, both of which take part in the biosynthesis and degradation in its metabolism. Concerning such pyrimidine nucleoside phosphorylase genes, cDNAs have been isolated from mice and human, and elucidation of their differences in expression is now under way on the gene level [Uchida et al., J. Biol. Chem., 270, 12191-19196 (1995); Uchida et al., Biochem. Biophys. Res. Commun., 216, 265-272 (1995)].
On the other hand, nucleoside antimetabolites which are playing an important role in the field of cancer chemotherapy in recent years are known to be inactivated by pyrimidine nucleoside phosphorylase due to their chemical structures. For the development of drugs excellent in pharmacological effects and low in side effects, it is therefore considered to be necessary to accurately grasp the mechanism of metabolism of these substances by pyrimidine nucleoside phosphorylase.
Uridine phosphorylase and thymidine phosphorylase are, however, observed to have substantial differences in their distribution depending on species. In human, thymidine phosphorylase are expressed in both normal tissues and tumor tissues, whereas in rodents such as mice and rats, uridine phosphorylase is primarily expressed centering around digestive tracts and thymidine phosphorylase is expressed only in some tissues such as livers. This has led to a problem in that the utility and the like of nucleoside anticancer agents in human cannot be precisely predicted from data on rodents.
On the other hand, thymidine phosphorylase is known to function as an angiogenic factor. It has recently been identified as a causative gene of MNGIE, a mitochondrial disease.
Accordingly, uridine phosphorylase expression deficient animals, if available in a phyletic lineage, will be useful as experimental animals for the study of physiological functions of the protein, for the elucidation of its related diseases, and also for the development and research of pyridine nucleoside antimetabolites (anticancer agents).
An object of the present invention is to provide a uridine phosphorylase expression deficient non-human animal or its offspring, which can be used as an experimental animal.
With the foregoing current circumstances in view, the present inventors have proceeded with research in various ways on mutation of a uridine phosphorylase gene, designing of a targeting vector, and so on. As a result, the present inventors have succeeded in creating a transformed animal having a uridine phosphorylase gene which practically does not function, and its offspring, leading to the completion of the present invention.
Specifically, the present invention provides a non-human animal deficient in a function of a uridine phosphorylase gene on a chromosome, or an offspring thereof.
As a result of developments in genetic engineering in recent years, it has become possible to artificially manipulate various genes and to create various transformed animals artificially added with foreign genetic characteristics or controlled in the expression of genetic characters which the organisms inherently possess [Nature, 300, 611-615 (Dec. 16, 1982); Proc. Natl. Acad. Sci. USA, 87, 7688-7692 (October 1990), etc.]. However, animals which are deficient in the function of a uridine phosphorylase gene on a chromosome and are genetically stable are not known to date.